As indicated by its hyphenated name, Nilo-Saharan is a family of the African interior, including the greater Nile basin and the central Sahara desert. Eight of its proposed constituent divisions (excluding Kunama, Kuliak and Songhay) are found in the modern two nations of Sudan and South Sudan, through which the Nile River flows.

In his book The Languages of Africa (1963), Joseph Greenberg named the group and argued it was a genetic family. It contains the languages not included in the Niger–Congo, Afroasiatic or Khoisan groups. It has not been sufficiently demonstrated that the Nilo-Saharan languages constitute a valid genetic grouping, and some linguists have seen the phylum as "Greenberg's wastebasket", into which he placed all the otherwise unaffiliated non-click languages of Africa.[1][2] Its supporters accept that it is a challenging proposal to demonstrate but contend that it looks more promising the more work is done.[3][4][5]

Some of the constituent groups of Nilo-Saharan are estimated to predate the African neolithic. Thus, the unity of Eastern Sudanic is estimated to date to at least the 5th millennium BC.[6] Nilo-Saharan genetic unity would necessarily be much older still and date to the late Upper Paleolithic.

This larger classification system is not accepted by all linguists, however. Glottolog (2013), for example, a publication of the Max Planck Institute in Germany, does not recognise the unity of the Nilo-Saharan family or even of the Eastern Sudanic branch; Georgiy Starostin (2016) likewise does not accept a relationship between the branches of Nilo-Saharan, though he leaves open the possibility that some of them may prove to be related to each other once the necessary reconstructive work is done.

Nubian (1.7 million, all dialects). The language of Nubia, extending today from southern Egypt into northern Sudan. Many Nubians have also migrated northwards to Cairo since the building of the Aswan Dam.

The total for all speakers of Nilo-Saharan languages according to Ethnologue 16 is 38–39 million people. However, the data spans a range from ca. 1980 to 2005, with a weighted median at ca. 1990. Given population growth rates, the figure in 2010 might be half again higher, or about 60 million.

The Saharan family (which includes Kanuri, Kanembu, the Tebu languages, and Zaghawa) was recognized by Heinrich Barth in 1853, the Nilotic languages by Karl Richard Lepsius in 1880, the various constituent branches of Central Sudanic (but not the connection between them) by Friedrich Müller in 1889, and the Maban family by Maurice Gaudefroy-Demombynes in 1907. The first inklings of a wider family came in 1912, when Diedrich Westermann included three of the (still independent) Central Sudanic families within Nilotic in a proposal he called Niloto-Sudanic;[9] this expanded Nilotic was in turn linked to Nubian, Kunama, and possibly Berta, essentially Greenberg's Macro-Sudanic (Chari–Nile) proposal of 1954. In 1920 G. W. Murray fleshed out the Eastern Sudanic languages when he grouped Nilotic, Nubian, Nera, Gaam, and Kunama. Carlo Conti Rossini made similar proposals in 1926, and in 1935 Westermann added Murle. In 1940 A. N. Tucker published evidence linking five of the six branches of Central Sudanic alongside his more explicit proposal for East Sudanic. In 1950 Greenberg retained Eastern Sudanic and Central Sudanic as separate families, but accepted Westermann's conclusions of four decades earlier in 1954 when he linked them together as Macro-Sudanic (later Chari–Nile, from the Chari and Nile watersheds). Greenberg's later contribution came in 1963, when he tied Chari–Nile to Songhai, Saharan, Maban, Fur, and Koman-Gumuz and coined the current name Nilo-Saharan for the resulting family. Lionel Bender noted that Chari–Nile was a historical artifact of the discovery of the family, and did not reflect an exclusive relationship between these languages, and the group has been abandoned, with its constituents becoming primary branches of Nilo-Saharan—or, equivalently, Chari–Nile and Nilo-Saharan have merged, with the name Nilo-Saharan retained. When it was realized that the Kadu languages were not Niger–Congo, they were commonly assumed to therefore be Nilo-Saharan, but evidence for this has not been presented.

Although progress has been made since Greenberg established the plausibility of the family, Nilo-Saharan has not been demonstrated. Koman and Gumuz remain poorly attested, and so are difficult to work with, while arguments continue over the inclusion of Songhai. Blench (2010) believes that the distribution of Nilo-Saharan reflects the waterways of the wet Sahara 12,000 years ago, and that the protolanguage had noun classifiers, which today are reflected in a diverse range of prefixes, suffixes, and number marking.

Dimmendaal (2008) notes that Greenberg (1963) based his conclusion on sound evidence, and that the proposal as a whole has become more convincing in the decades since. Mikkola (1999) reviewed Greenberg's evidence and found it convincing. Roger Blench notes morphological similarities in all putative branches, which leads him to believe that the family is likely to be valid.

Koman and Gumuz are poorly known and have been difficult to evaluate until recently. Songhay is markedly divergent, probably due to massive influence from the Mande languages. Also problematic are the Kuliak languages, which are spoken by hunter-gatherers and appear to retain a non-Nilo-Saharan core; Blench believes they may have been similar to Hadza or Dahalo and shifted incompletely to Nilo-Saharan.

Anbessa Tefera and Peter Unseth consider the poorly attested Shabo language to be Nilo-Saharan, though unclassified within the family due to lack of data; Dimmendaal considers it to be a language isolate on current evidence. Proposals have sometimes been made to add Mande (usually included in Niger–Congo), largely due to its many noteworthy similarities with Songhay rather than with Nilo-Saharan as a whole.

The extinct Meroitic language of ancient Kush has been accepted by linguists such as Rille, Dimmendaal, and Blench as Nilo-Saharan, though others argue for an Afroasiatic affiliation. It is poorly attested.

There is little doubt that the constituent families of Nilo-Saharan—of which only Eastern Sudanic and Central Sudanic show much internal diversity—are valid groups. However, there have been several conflicting classifications in grouping them together. Each of the proposed higher-order groups has been rejected by other researchers: Greenberg's Chari–Nile by Bender and Blench, and Bender's Core Nilo-Saharan by Dimmendaal and Blench. What remains are eight (Dimmendaal) to twelve (Bender) constituent families of no consensus arrangement.

By 2000 Bender had abandoned the Chari–Nile and Komuz branches, added Kadu, and removed Kuliak from Eastern Sudanic. He stated that Shabo could not yet be adequately classified, but might prove to be Nilo-Saharan.

With a better understanding of Nilo-Saharan classifiers, and the affixes or number marking they have developed into in various branches, Blench believes that all of the families postulated as Nilo-Saharan belong together. He proposes the following tentative internal classification, with Shabo possibly closest to Koman and Gumuz, and Songhai closest to Saharan, a relationship that had not previously been suggested:

By 2015,[10] and again in 2017,[11] Blench had refined the subclassification of this model, linking Maban with Fur, Kadu with Eastern Sudanic, and Kuliak with the node that contained them, for the following structure:

Georgiy Starostin (2016),[14] using lexicostatistics based on Swadesh lists, is slightly more inclusive than Glottolog, and in addition finds probable and possible links between the families that will require reconstruction of the protolanguages for confirmation.

In addition to the families listed in Glottolog (previous section), Starostin considers the following to be established:

A relationship of Nyima with Nubian, Nara and Tama (NNT) is considered "highly likely" and close enough that proper comparative work should be able to demonstrate the connection if it's valid, though it would fall outside NNT proper (see Eastern Sudanic languages).

Other units that are "highly likely" to eventually prove to be valid families are:

Possible further "deep" connections, which cannot be evaluated until the proper comparative work on the constituent branches has been completed, are:

Eastern Sudanic + Fur + Berta

Central Sudanic – Kadu + Maba–Kunama

There are faint suggestions that Eastern and Central Sudanic may be related (essentially the old Chari–Nile clade), though that possibility is "unexplorable under current conditions" and could be complicated if Niger–Congo were added to the comparison. Starostin finds no evidence that the Komuz, Kuliak, Saharan, Songhai or Shabo languages are related to any of the other Nilo-Saharan languages. Mimi-D and Meroitic were not considered, though Starostin had previously proposed that Mimi-D was also an isolate despite its slight similarity to Central Sudanic.

Proposals for the external relationships of Nilo-Saharan typically center on Niger–Congo: Gregersen (1972) grouped the two together as Kongo–Saharan. However, Blench (2011) proposed that the similarities between Niger–Congo and Nilo-Saharan (specifically Atlantic–Congo and Central Sudanic) are due to contact, with the noun-class system of Niger–Congo developed from, or elaborated on the model of, the noun classifiers of Central Sudanic.

Nilo-Saharan languages present great differences being a highly diversified group. It has proven difficult to reconstruct many aspects of Proto-Nilo-Saharan language, and many authors remain skeptical about the validity of the family. Two very different reconstructions of the proto-language have been proposed, by Lionel Bender and Christopher Ehret.

The phonemes /*d2, *t2/ correspond to coronal plosives, the phonetic details are difficult to specify, but clearly, they remain distinct from /*d, *t/ and supported by many phonetic correspondences (another author, C. Ehret, reconstructs for the coronal area the sound [d̪], [ḍ] and [t̪], [ṭ] which perhaps are closer to the phonetic detail of /*d2, *t2/, see infra)

Bender gave a list of about 350 cognates and discussed in deep the grouping and the phonological system proposed by Ch. Ehret. Blench (2000) "The classification of Nilo-Saharan", p. 299[dead link] compares both systems (Bender's and Ehret's) and prefers the former because it is more secure and is based in more reliable data. For example, Bender points out that there is a set of phonemes including implosives /*ɓ, *ɗ, *ʄ, *ɠ/, ejectives /*pʼ, *tʼ, (*sʼ), *cʼ, *kʼ/ and prenasal constants /*mb, *nd, (*nt), *ñɟ, *ŋg/, but it seems that they can be reconstructed only for core groups (E, I, J, L) and the collateral group (C, D, F, G, H), but not for Proto-Nilo-Saharan.

This maximalist system has been criticized by Bender and Blench. These authors state that the correspondences used by Ehret are not very clear, and because of this many of the sounds in the table may only be allophonic variations.[citation needed]